This invention relates to suspension polymerization processes and in particular to the suspending agents employed in said processes.
Various water-soluble polymers such as polyacrylamide and copolymers of acrylamide with other anionic, cationic or nonionic monomers are well-known to be precipitants or flocculants for many substrates including sewage, cellulosic fibers and fines for retention and freeness, effluent waste for metal production, coal tailings and the like. Such polymers are also known to exhibit superior thickening properties when said polymers are dissolved in aqueous media. Particularly well known for this purpose are the anionic polyacrylamides such as acrylamide/acrylic acid copolymers, including those prepared by hydrolysis of polyacrylamide. Such polymers are also very useful as fluid mobility control agents in enhanced oil recovery processes.
In the past, such polymers have been made available commercially as powders or finely divided solids which must be subsequently dissolved in an aqueous medium in order to be used. Because such dissolution steps are sometimes time consuming and often require rather expensive mixing equipment, it has become a common practice to formulate the water-soluble polymers in water-in-oil emulsions wherein the polymer is dissolved in the dispersed aqueous phase. Such emulsions, as well as methods for preparing them, are described in U.S. Pat. Nos. 3,284,393; 3,826,771 and 4,052,353.
More recently, it has become desirable to provide aqueous fluid absorbents by polymerizing water-soluble monomers such as acrylic acid in the presence of a crosslinking agent in order to provide highly swellable polymeric materials. Such types of aqueous fluid absorbents and materials provided therefrom are disclosed in U.S. Pat. Nos. 4,511,477; 4,500,670; 4,424,247; and 4,293,609. Due to the nature of the crosslinking agents employed in the preparation of such aqueous fluid absorbents, the use of water-in-oil emulsion polymerization technology in providing such types of polymeric materials has not been successfully employed to any great extent.
Suspension polymerization processes provide several advantages in the preparation of water-soluble polymers and water-swellable polymers. The reaction temperature and rate of reaction can be controlled due to the heat transfer properties attendant in such types of polymerization processes. For example, the reaction temperature can be controlled by means of ebullient cooling. In addition, the polymer product so provided in water-in-oil suspension polymerization processes can be separated from the oil phase using relatively efficient techniques such as filtration or centrifugation. However, improvements in the preparation of water-soluble polymers and water-swellable polymers is clearly desirable.
In view of the deficiencies of the prior art, it would be highly desirable to provide a process for polymerizing water-soluble monomers using water-in-oil suspension polymerization techniques; which process is capable of employing high quantities of monomer in the aqueous phase without substantial agglomeration of polymer, and which process can be employed in providing crosslinked water-swellable polymers of a controlled particle size.